Synchronous communication system



y 7,1940- H; J. mcHoLs 2,199,546

SYNCHRONOUS COMMUNIGAT I ON SYSTEM OriginalFiled May 22, 1933 ssheets-sheet 1 T Pn/zvrzR-si s fly. 1-14 BY 4&-

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SYNCHRONOUS CQMMUNICATION SYSTEM briginal Filed May 22. 1953 aSheets-Sheet. 2

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y 7, 1940- H. 'J. NICHOLS 1 2.199546 SYNCHRONOUS COMMUNICATiQN SYSTEMOriginaIFiled ma 22, 1933 s Sheets-Sheet s [Wil I92 M i ia: 7

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smrmonous COMMUNICATION SYSTEM I Ori inal Fild May 22, 19s: aSheets-Sheet, 4

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' SYNCHBONOUS COMMUNICATION SYSTEM Y driginal Filed May 22, 19s: aSheets-Sheet e N w I E Q I Diaplacement y 1940- H. J. NICHOLS 2.199.546

SYNCHRONDUS COMMUNICATION SYSTEM Original Filed May 22, 1933 8Sheets-Sheet 7 IN VEN-TOR. j W Muss s.

y 7, 1940- I H. J. NICHOLS 2.199.546

SYNCHRONOUS COMMUNI A'I'IQN SYSTEM ori inal-"Filed Ma 22, 19s: aSheets-Sheet s Patented May 7, 1940 2,199,546 SYNCHRONOUS COMMUNICATIONSYSTEM PATENT OFFICE Harry J. Nichols, Binghamton, N. Y., assignor toInternational Business Machines Corporation, New York, N. Y., acorporation of NewYork Original application May 22, 1933, Serial No.

672,161, now Patent No. 2,104,570, dated January 4, 1938-.

Divided and this application -March 25, 1937, Serial No. 132,927

7 Claims.

This invention relates to synchronous communication systems andparticularly to single impulse printing telegraph systems and is adivision of the copending application Serial No. 672,161, filed May 22,1933, patented Jan. 4, 1938, No. 2,104,570.

A general object of the invention 'is to provide a printing telegraphsystem in which single signal impulses, distinguished only in respect totime, are utilized to automatically establish synchronism, to providecontinuous phase correction to maintain synchronism, and to select theprinting characters and printing movements.

A more specific object is to provide a synchronizing and selectivesystem, and suitable apparatus, whereby an electric typewriter, withminor modifications and changes, can be utilized as the printingmechanism of a printing telegraph.

A further object is to provide a printing telegraph system in which thegreater part of the" apparatus is utilized for both sending andreceiving functions with consequent advantages in economy. and insimplification.

A further object is to provide a printing telegraph system in which bythe simple manipulationby the operator of a single switch, the apparatusis instantly placed inthe sending, receiving, or typing condition.

A further object is to provide printing telegraph apparatus utilizing astandard typewriter keyboard and with both lower case and upper caseletters, figures, and characters, with automatic operation of carriagereturn, shift, spacer, tabulator, and back spacer, etc. so thattelegraphic communications may be transmitted in the form of the usualcommercial or personal letter. A further object is to provide printingtelegraph apparatus of the speed, touch, and keyboard of a standardtypewriter so that typists trained to operate the ordinary typewritermay, without special training, operate the printing telegraph apparatusdescribed in the present invention.

A feature of the present invention is that the typewriter utilized asthe printing mechanism of the printing telegraph system hereindisclosed, when not being used for the transmission or reception ofmessages, is equally suitable for typing letters, reports, etc. of theusual nature.

A further object of the present invention is a simple calling signallingarrangement whereby initial calls can be made whether or not the drivingmotor is running, and while the typewriter is being-used for typing, andbreak-in calls can be made during transmission. the same appara: tusbeing utilized to eifect calling signals under the several conditions.

.A further object of the invention is to automanner and with exactness,synchronism between transmitting and receiving apparatus at separatepoints.

A further object is to accomplish such synchronism by means of singleimpulses transmitted at a definite phase position during each cycle ofmotion of the transmitting apparatus. A further object is to accomplishsuch syn chronisin by means of signal impulses suitable for transmissionover telephone, telegraph, or .radio communication systems withoutspecial adaptation of such systems. A further object is to maintainclose synchronism of the receiving apparatus by correcting, ifnecessary, and in. the degree necessary, the phase position of thecontrolled element once during each cycle of motion, ensuring that thecontrolled element moves at all times in close synchronism with thecontrolling element.

A further object is to provide a governor for driving motors for thesynchronized elements which is accurate, sensitive, and quick inresponse, and which is compensated for tempera- A further object is-toprovide a governor for the driving motor which permits. minor speedadjustments to be made electrically without ad-' justment of themechanical settings 01' the governor and without impairing the range ofoperation and accuracy of regulation of the governor.

A further object is toprovide a motor speed control arrangementwherebymeans operable from a distance may be utilized to efl'ect a minoradjustment of the motor speed in -a predeter-' loss of control by theand which resumes the unoperated condition, 7

when a single periodic impulse is missed.

A further object'is to provide a phase vcorrecting mechanism which issimple in construction, accurate in operation, reliable and-durable, and

which automatically compensates for instrumental and line retardation ofsignals.

A further object is to provide a smooth -'acting phase corrector whichwhile in continuousoper ation, will not tend to change the speed of thecontrolled element when running in synchronism.

A further object is to provide anelectromagnetic phase corrector whichfunctions to correct the phase position of the controlled elementwithout physical engagement therewith.

A further object is to provide non-repeat means in the sending conditionwhereby only one signal is sent to the line for each operation of a typebar key lever.

A further object is to provide interlock means whereby only one keylever may be depressed at a time.

A further-object is to provide a key latch and key release means wherebyduring sending operations, a key lever when depressed is retained inthat position until the rotary distributor collects the correspondingsignal, whereupon the key lever is released for return to the unoperatedposition.

A further object is to provide means ,whereby the key latch is held outof engagement with the key levers after release by collection of ,thesignal, and thereafter as long as the key is held depressed manually,and is permitted to return to the position of engagement with all keylevers when the held key is released.

A further object is to provide automatic cut-off be considered as partsof the same drawin show in diagrammatic form the circuits and apparatuswhich together with'the typewriter or printer comprise a completecommunication unit. Fig. 1A shows the circuits and apparatus utilized insending, receiving, and calling. The circuits are shown in the "typingcondition, which is the condition when the selector apparatus is notbeing used for sending and receiving, and the typewriter is availablefor typing. Fig. 1B shows the power rectifier providing power for thevarious relays, magnets, etc. comprising the selecting ap- '50 paratus,and 'the distributor driving motor and its control.

Fig. 2 shows in diagrammatic form the circuits and apparatus utilized insending, and for purposes of explanation is referred to as the sendinstation or station "A".

Fig. 3 is a similar diagram of the circuits and apparatus utilized inreceiving, and is referred to as the receiving station or station B-Fig. 4 is a similar diagram of the circuits and apparatus used incalling.

Fig. 5 is a plan view of the rotary distributor assembly including theplateau with segments and ring, the rotating distributor arm, and thecor- .rector magnet in relation to the distributor,

' preparatory for release to establish synchronlsm. Fig. 6 is a. sideview, partly in section, showing the same assembly as in Fig. 5 anddetails of the hub, drive shaft, and friction drive. I

"Fig. -7 is a sectional view on line VIIVII of Fig. 6, looking towardsthe corrector magnet.

Fig. 8 is a side view showing a modification of the correctorarrangement, in which the corrector bar passes across the face of thecorrector magnet 75 poles.

showing the distributor arm in the rest position Fig.- 9 is a plan viewof the structure shown in Fig. 8.

Fig. 10 is a side view showing a further modification of the correctorarrangement.

Fig. 11-is aside perspective view of the corrector bar shown in Fig. 10.

' Fig. 12 is a pull-displacement diagram showing the general nature ofthe tangential magnet pull on the corrector bar by the corrector magnet.

Fig. 13 is a plan view of the electromagnetic clutch arrangement shownin the rest position.

Fig. 14 is a similar view, omitting the clutch magnet, and showing theclutch cam position for free rotation of the distributor hub.

Fig. 15 is a side view of the cam mechanism assembly shown in Fig. 14.

Fig. 16 is a cross section view of the clutch cam taken on line XVIXVIof Fig. 13.

Fig. 17 is a schematic circuit diagram, showing the part of the circuitassociated with the clutch relay magnet.

Fig. 18 is an end view of the governor assembly.

Fig. 19 is a side view of the governor assembly.

Fig. 20 shows, in exaggerated form, the efiect of temperature on thethermal compensation means for the governor. I

Fig. 21 is a diagram showing schematically the arrangement for minoradjustment of the motor speed.

Fig. 22 is a fragmentary view of the key interlock, illustrating theprinciple of operation.

Fig. 23 is a side view, partly in section, of the solenoid assembly, thekey interlock, and the key latch, showing the construction andarrangement of these parts. The spring link for connecting the plungersof the solenoids to the members which they actuate is also shown.

Fig. 24 shows the left end of the space bar assembly, showing thedetails of construction.

Like characters represent like parts.

General description,

A complete installation unit consists of an elec tric typewriter, atypewriter control assembly, and a distributor unit assembly. Thetypewriter control assembly is mounted underneath and inside thetypewriter frame. The distributor unit assembly is housed in a case, andis located near the typewriter. The two assemblies are connectedelectrically by a multiple conductor cable.

The principal items of equipment comprising a typewriter controlassembly are:

(a) The key solenoid assembly. (1)) The key switches.

(c) The auxiliary switch.

(d) The key latch. (e) The key latch release magnet.

(f) The key interlock.

In Fig. 1A, the apparatus comprising the typewriter control assembly isincluded within the rotary distributor.

dot-dash rectangle. All other apparatus is in? cluded in the distributorunit.

The apparatus shown in Fig. 1A performs the functions of transmittingand receiving printing impulses and synchronizing impulses, both ofwhich classes of impulses are distributed via the Referring to Figs. 1,5, 6, therotary distributor consists of a series of metallicsegments II,and solid metallic ring I2, both mounted on a disk It of insulatingmaterial, and the rotary brush arm I3, rotatably mounted on and,yieldingly driven by the drive shaft 55. The ring and segments, whileac tually arranged in concentric circles, are shown in lineardevelopment in some figures in order to simplify the diagram. The rotarybrush arm I3, which makes electrical connection from ring to segments,passes across all the segments once during each resolution in a wellunderstood manner. The drive shaft 55 is conveniently driven at uniformspeed by a motor 99, as hereinafter described. The brusharm I3 is shownin-the rest position on segment 3.

A clutch release relay I5 is provided to stop and to release the brusharm in accordance with the invention, and for illustrative purposes isshown with its armature I6 in engagement with the brush arm I3. Thearmature I6'also actuates springs I1 and I3 which function in connectionwith receiving operations.

The release relay I5 is provided with a low impedance winding 29 and ahigh impedance winding 2I connected in series. Across the terminals ofthe winding 2I' is connected a storing condenser 22. ,The outer terminalof the winding 29 is connected'to the positive bus 26; the

outer terminal of winding 2| is connected tospring I8, to spring I92 ofthe send-receive switch I96, and to one terminal of the corrector magnet36. The release relay I6 is of .the quick acting, slow release type, andresponds quickly to a short current impulse, but holds for a pro--longed period, and if supplied with properly timed impulses continues tohold in the operated position as long as such impulses are regularlyreceived. A relay which so operates is sometimes called a pulsesustained relay, and while other forms of such relays are in use, theparticular form here disclosed is novel and constishown in Fig. 1B. Therectifier assembly con-: sists of the power transfer 2"], rectifier tube2, preferably of full-wave type as shown, the filter condenser 2I2, andfilter choke 2I3, all

connected as shown. The power transformer 2III has a primary 2,connected to the power mains I 2I1; secondary 2|! to supply heatingcurrent to the cathode'of tube 2I I; center tapped secondary 1 M6 tosupply-anode 'current'to the tube 2| I; and secondary I 31 with centertap I36 to supply heat ing current to the cathode of the electronicrelay The output of the rectifier is applied to theterminals of thevoltage divided 24a and 24b shown in Fig. 1A. The positive bus 26 isconnected to the positive terminal of the voltage divider, and thenegative bus 26 to the negative terminal. 'The zero bus I3I is connectedto the zero terminal between'sections 24a and 24b of the voltagedivider,-the section 2411 thus furconnected to the zero bus I3I.

In series with the plate I35 of electronic relay I32 is the cut-offrelay I10, connected as shown, with winding I'II shunted by variableresistor I12, and providedwith contacts I13 and I". As

is well known, the grid of. a grid controlled gaseous discharge tube isusually unable to stop the discharge when once started. and the plate.current is normally cut off by disconnecting the plate supply, or bycausing the plate to become primary winding 26 and secondary winding 29;

and the receiving or input transformer 32 with center tapped primary 33and secondary 34. The resistor 35, of a suitable value to balance theline impedance, is connected across the secondary 34, and across thisresistor 35 appears the potential which overbalances the normal bias onthe grid I33, and trips off the electronic relay in a well understoodmanner. The center tap of the primary 33 is connected to one terminal ofthe secondary 29, the other terminal being connected to the lineterminal 30.

One terminal of the primary 33 is connected to the terminal 39 while theother terminal is connected to line terminal 3I through the artificialline network AL as shown. Y The functioning of duplex transmission beingwell understood, the operation is manifest and does not requirediscussion beyond that which will be given hereafter in connection withthe calling circuits. f

The send-receive switch I99 is a three position switch, the threepositions being indicated by RTS, referring respectively to thereceiving, typing, and sending conditions. The switch is of the levertype and has one set of break-make springs, and one set of make springs.These springs are numbered from I9I to I inclusive. In the T and Spositions, the send-receive switch mechanically holds the universal barkey latch IiiI out of engagement with the key levers I66."

The multiple switch relay I60, controlled by the send-receive switchI99, provides the a1 ito-' maticswitching operations required to changefrom sendinglcondition to receiving condition and, vice'f versa. It isprovided with a single windingfI6I, and three sets of'break-makecontacts numberedfrom I to 9 inclusive. In order to simplify thediagram, these contacts are shown in their natural locations in thecircuit, and

are numbered I to 9 inclusive for the purpose The purpose of the readingcondenser'arran ge- 1 pensates in part the inductance of the circuit ofwhich it is a part.

Synchronization Referring to Fig. 2, the transmission of synchronizingimpulses is accomplished as follows:

Assume that the brush arm I3 is frictionally driven, but is held in therest position on segment 3 by the armature I6 of the relay I5. To startsending synchronizing signals, the sendreceive switch I90 is thrown tothe S position, as indicated. This completes a circuit from zero busthrough reading condenser I62 through winding I 6| of multiple switchrelay via contacts Nil-I92 of send-receive switch to relay I5, throughcondenser 22 and winding 20 to positive bus. A strong current throughthis circuit operates multiple switch relay I60, breaking contacts 2-3,56, 8--9 and making contacts I2, 4-5, 1-8. Release relay I5 is alsoenergized, attracting armature I6 which releases brush arm I3. Ascondensers 22 and I62 become charged, a small steady current limited byresistor I63 flows through windings I6I and 2| providing sufficientholding current to hold the multiple switch relay and release relay inthe operated condition. A strong operating pulse followed by low holding.current is thus provided, preventing over heating of the relaywindings.

On being released by armature I6, the brush arm I3 is set in rotation bythe friction drive, and takes up the uniform speed of the drive shaftset by the driving motor. When the brush arm reaches segment I, acircuit is completed from positive bus via contacts 81 through the pulseshaping network comprising the reading condenser. I65 and shunt resistorI66 and inductance I61 in series therewith,via contacts 4-5 to segmentI, via brush arm I3 to ring I2, via contacts 2I through primary 28 tozero bus. For the duration of the contact of the brushes with segment I,current flows through the circuit just traced, a corresponding signalimpulse is sent to the line by the, secondary 29 of the outputtransformer 21. This impulse, which is repeated for each revolution ofthe brush arm I3, is called the synchronizing signal.

It is to be noted that the synchronizing signal in its passage to theline from secondary 29 passes through primary 33 via the center tap, andthus through the equal sections of primary 33 to the line terminals.With the artificial line AL in proper balance the currents through thesections of primary 33 are equal, and in opposition, hence no voltage isinduced in the secondary 34 and the grid I33 is unaffected by signalssent to the line under these conditions.

Referring to Fig. 3, the reception and application of the synchronizingsignals at the receiving station is as follows:

At the receiving station, the synchronizing signals are received at theline terminals 30 and 3| and are applied to the terminals of primary 33of the input transformer 32. The current from terminal 30 passingthrough the secondary 29 of the output transformer and the center tapbranch of primary 33 is negligible.

The synchronizing signal through primary 33 induces a voltage across.secondary 34 and shunt resistor 35, which with proper polarity of theline terminals, opposes the bias voltage on grid m. The potential ofgrid m is thus made I5 will be more fully described hereinafter.

more positive and at a critical value depending on the characteristicsof the relay I32 and the plate voltage thereon, relay I32 becomesionized and conducting, and current fiows in the plate circuit. Thebrush arm I3 being at rest on segment 3, a circuit is completed fromzero bus through center tap I36, and transformer winding I31 throughcathode I34 to plate I35 via contacts I13-I14 through winding I1I viacontacts I94I95 of the send-receive switch and contacts 3-2 to ring, viabrush arm I3 to segment 3 via contacts I1I8 through condenser 22,through Winding 20 to positive bus. A strong current pulse flows throughthis circuit, operating release relay I5 and thereafter cut-off relayI10, which opens contacts I13-I14, terminating the pulse. The armatureI6 is pulled in, releasing the brush arm I3, and opening contacts I1I8.The flow of current through condenser 22 has charged that condenserproviding holding current for the-high impedance winding 2I, delayingthe release of armature I6. The cut-off relay I10 releases quickly,being of low impedance, and being shunted by the resistor I12. Beforerelay I10 closes its contacts, however, the plate current has beeninterrupted long enough to permit the electronic relay I32 to de-ionizeand the grid I33 to regain control. The electronic relay I32, with itsassociated cut-off relay, thus provides strong local current impulseswhich are initiated by the line signals, but which are of definiteduration.

When released, the brush arm I3 is set in motion by its friction drive(and clutch as is explained hereinafter) and is thereafter rotated atuniform speed. Brush arm I3 having started from segment 3 shortly afterthe brush arm at the sending station passed segment I, would arrive atsegment I before the arrival of the next synchronizing signal from thesending station, were it not for a slight delay in the operation ofrelease relay I5 and the clutch mechanism.

Because of these delays which occur only during the first revolution,the lead provided by starting the brush arm from rest on segment 3enables the brush arm to arrive at segment I as the next synchronizingsignal is received. The synchronizing signal energizes the electronicrelay I32 as before, but this time the circuit is completed via segmentI as follows: via same circuit as before to ring, via brush arm tosegment I, via contacts 5-6, through winding of corrector magnet 36,through condenser 22 and winding 20 to positive bus. The current pulsethrough this circuit replenishes the charge on condenser 22, maintainingthe release relay I5 in the operated condition, and energizes thecorrector magnet 36. The details of the operation of the correctormagnet 36 and release relay At this point it is to be observed thatprovided the brush arm I3 arrives on segment I when the synchronizingsignal is being applied to the grid of the electronic relay, the chargeon the condenser 22 is replenished, sustaining the operation of therelease relay I5, and the corrector magnet 36 is energized. If theseconditions are not fulfilled, release relay I5 drops out, and during thesubsequent revolution the brush arm I3 is stopped on the rest segment.If the signals continue, the same procedure is repeated untilsynchronism is established.

In practice, it is found that with proper adjustment of the-clutchmechanism and by setting the rest position for the brush arm at theproper place, synchronism is usually established on the firstrevolution. Thereafter, synchronism if maintained by the correctormagnet correcting the phase angle of the receiving distributor arm tokeep it in unison with the sending distributor arm. Should, for anyreason, unison within approximately one half segment width be departedfrom, the brush arm I3 is stopped on the rest segment by reason ofrelease relay I5 dropping out, and the synchronizing procedure isrepeated when the next synchronizing pulse is received. Thussynchronism, if lost, is automatically re-established.

Sending circuits and operations Referring to Fig. 2, the printing signalimpulse I transmitting apparatus includes the key switches I51 ofbreak-make type, one for each key of the typewriter,- there being 49keys on a standard typewriter keyboard. The armature spring of each keyswitch is connected to an individual Each key lever operates itsassociated key switch by means of an insulated push rod I50 asindicated. For transmitting purposes, each key lever when depressed isheld down by the universal bar key latch I5I until released by'the keyrelease magnet I52. The universal bail I53 is positioned below andtransversely across the row of key levers, being held in light contacttherewith by a retractile spring (not shown). When any key is depressed,'the bail I53. closes the auxiliary switch I54 by means of push rod I55;One spring of the auxiliary switch is connected to the key switch busI38; the other spring is connected to spring I42 of non-repeat relayI40.

' The non-repeat relay I40 has a low impedance winding I4B,.located onthe heel .end of the core I40, and a high impedance winding I41. Inseries with the winding I41 is a reading condenser arrangementconsisting of the condenser I48 and shunt resistance I48.

To commence sending, the send-receive switch is thrown to the Sposition, and synchronizing signals are sent to the line for a fewseconds to permit the-receiving machine to cometo synchronism asdescribed above. Printing signals may be sent by depressing thetypewriter keys as for ordinary typing.

Assuming key 5 to be depressed, the operations which result are asfollows: As the key lever nears the bottom of its stroke, the mechanismof the typewriter is tripped, and the typewriter immediately types theselected character to fur-.

nisha local copy of the message. The key lever is latched down in thedepressed position by the universal bar keylatch I5I hooking over theend of the key lever I56. The finger can be at once removed'from thekey. When the key is pressed down, the push rod I50 .(one for each' keyswitch connects the key switch bus ,I38 to thesegment associated withthe particular key switch, in the present instance segment 5. When thebrush arm I8 arrives at segment 5, a circuit is completed from positivebus, via contacts 81 through low impedance winding I46 of non-repeatrelay I40, via contacts I44-I45 to key .switch bus I38, via middle andlower contacts of the operated key switch to segment 5, via brush arm I8to ring, via contacts 2I through primary 28 of output transformer 21 tozero bus I3I. A strong current impulse flows through this circuit, itsduration being determined by the time of contact of the brush arm I3with segment 5, and a printing signal of the same duration is sent'tothe line by the secondary 29 of the output transformer 21.

Non-repeat and key release arrangement The local current impulse justdescribed, in addition to sending a printing signal to the line, alsoperforms an important part in the non-repeat and key release actions.The local current pulse through winding I46 of non-repeat relay I40,together with the part of the pulse flowing through the high impedancewinding I41, operates non-repeat relay I40, thus opening contactsI44--I45, and closing contacts I44-I43, and I42 -I4'I. Opening contactsI44-I45 cuts off the winding I46. Closing contacts 4-443 connects oneterminal of the key release sole- .noid I52 to the key switch bus I38and to winding I41. Closing contacts I42-I4I connects the zero bus I3Ito the upper spring of the auxiliary switch and through its contactsplaceszero potential on the key. switch bus I38. Any connected segment,except thesynchronizing segment, is therefore likewise placed at zeropotential and no more printing signals can be sent to the line. Thisconstitutes the non-repeat feature.

Closing contacts I42-I4I also completes a circuit from negative bus viacontacts I4II42, via contacts of the auxiliary switch, through windingI41 and reading condenser I48 via contacts 8-1 to positive bus. Currentthrough this circuit reenergizes non-repeat relay I40 and suppliesholding current therefor. A second circuit is com- -'pleted frompositive bus via contacts 8-1 through the winding of the key releasesolenoid I52, through reading condenser I18 via contacts -I43I44, viaauxiliary switch contacts, via contacts I42-I4I to zero bus. A currentpulse through this circuit energizes the key release solenoid I52, whoseplunger pulls the key latch I5I away from the key levers by means of'the extension I82 as shown. r

If the'flnger is removed from the freed key, the key lever is drawn upby its retractile spring and the-springs of the auxiliary switch I54lift the push rod I55 and open the contacts.

Opening these contacts breaks the circuit ,to

zero bus via contacts I42-I4I, and takes theholding current from thenon-repeat relay I40 and key release solenoid I52, which thereuponrelease. Zero potential is also removed from the key switchbus I38 andany connected segment. When the key release solenoid I52 releases, thekey latch I5I is returned to an engageable position by the retractilespring I83. When the n'oncontacts I4I-I43 and liberately held down,repeat signals are not perparatus nor as regards the accuracy of trans-'mission. In normal operation the keys are depressed and released quicklyby the operator, and are released by the key-release solenoidpractically instantaneously when the printing signal is sent to theline.

Key interlock It will be apparent fromthe foregoing description ofsending operations, that a variable interval intervenes between theclosing of a key switch and the collection of the impulse from theconnected segment by the distributor brush. This interval depends on thespeed at which the distributor rotates and the angular travel of thebrush arm in order to reach the connected segment, the interval beingalways less than the time of one revolution.

It is manifest that if two keys were pressed simultaneously, or almostsimultaneously, the distributor would send out a printing signal fromthe first connected segment, whether or not this was the proper orderfor transmission. To eliminate errors of this kind, a key interlock isprovided which permits only one key at a time to be depressed. Whilevarious forms of interlock have been devised and employed, the preferredform is shown in Figs. 22 and 23. This form of interlock is well known,and its operation being familiar to those current with the art, detaileddescription is not required.

The principal parts of the interlock are the comb 235, the roller race234, and the rollers 236, one for each key lever plus one. Each keylever is located in an individual slot in the comb 235 as shown. Thediameter of the rollers is exactly equal to the key space centers, andthe space between all the rollers combined is slightly greater than thethickness of a key lever I55. As indicated in Fig. 22, when one keylever is depressed, the slots for all the rest of the key levers areblocked.

Dual space segment arrangement With a single impulse system as hereindescribed, the duration of the signal impulse is determined by thenumber of segments on the distributor and the speed of rotation of thedistributor arm.

There is a practical lower limit to the duration of the signal impulse,since the shorter the impulse, the higher the required frequencycharacteristics of the transmission system connecting the sending andreceiving stations. As is well known, all communication systems havedefinite limits as to frequency characteristics, the

limits being particularly restricted on telegraph cable circuits. One ofthe limitations on the speed of operation of printing telegraphsystemsis therefore the length of the signal impulses and the number ofsegments on the distributor and the speed of rotation of the distributorarm are subject to this and other limitations.

One of the features of the present invention is the means by which thenumber of words transmitted'in a given time is increased without a Anaverage word in telegraphic practice consists of five letters and aspace, and the-speed of transmission is rated on the basis of the numberof equivalent average words sent per minute. On the average, since aspace occurs for every five letters, one sixth of the signals are spacesignals. In the present invention, means are provided whereby theaverage time required to collect and transmit a space signal isapproximately one half that required to collect and transmit otherprinting signals. The means is to provide two segments for the spacesignal located" approximately diametrically opposite on the distributor.These segments are connected in parallel, and either one can transmit orreceive a space signal. The arrangement is indicated by the connectionof segments 8 and 36 in Fig. 1A. Thus, when the space bar is depressed,the distributor arm on the average moves only one quarter revolutionuntil the signal is collected; for other signals an average movement ofone half a revolution is "required. As an example of the advantage ofthis improvement, assume that the distributor arm makes 4 revolutionsper second. The theoretical average speed of transmission, using onlyone space segment, would be:

Using the dual space segment arrangement, the theoretical average speedwould be:

4X60 87 words per minute (approx.)

Sine wane impulse feature As is well understood, a sine wave impulseundergoes the minimum distortion in transmission, and permits the designof circuits of minimum impedance for a given frequency. Also, theproblem of suppressing sparking at contacts is rendered less diffcult.One of the features of the present invention is means whereby virtualsine wave impulses are generated in the local circuits, and the signalssent to the line are of approximate sine wave form. In the sendingcircuit, the means for forming sine wave impulses comprise the storagecondenser I86 across the voltage divider 24a and in series with section24b, to-

gether with wave shaping arrangements and" proper design of the circuitconstants of inductance, resistance, and capacity. In the sendingcircuit connected to segment I for generating synchronizing impulses,the wave shaping arrangement comprises the reading condenser I65 andshunt resistor I66, and inductance I61 in series therewith, togetherwith the storage condenser |86 and the primary 28 of the outputtransformer 21, cooperate to produce a sine wave impulse in thiscircuit, and virtual sine wave synchronizing signals are sent to theline. In the printing signal circuits, the storage condenser I86, thereading condenser I48, windings M8 and 141 of non-repeat relay I40, andthe primary 23 cooperate to produce sine wave impulses in thesecircuits.

Receiving circuits and operations Synchronism having been established aspreviously described, and the brush arms at the receiving and sendingstations being in unison,

sister 35 opposing the negative bias on grid I33, which on becomingsufficiently positive triggers 011 the electronic relay I32 whichbecomes conducting. A circuit is thus completed from zero bus I 3|through center tap I35, and winding I31, from cathode I34 to anode I35,via contacts I'M-I14 through winding I1I, via contacts I34-I95, viacontacts 3-2 to ring, via brush arm I3 to the particular segment withwhich the 10 brushes of distributor arm. I3 are in contact. From thissegment, of which segment 5 may be considered as an example, the circuitcontinues via the middle and upper contacts of key switch I51 to windingI59 of key magnet I58 to key 15 magnet bus I39, thence via contacts 89to positive bus 25. The pulse through this circuit energizes cut-01frelay I10 and key. magnet I58, whose plunger is attracted, stretchingspring link I84 which pullsdown the key lever to'which it is 20attached. The key lever trips the typewriter mechanism (not shown)- andthe character is printed. As the key lever nears the end of its downwardtravel, the push rod I50 breaks the middle and upper key switchcontacts. Owing 25 to the inductance of the key magnet, the inertia ofthe plunger and the key lever, and the action of the spring link I84,the breaking of the key switch contacts is retarded and the circuit isactually broken by the opening of the contacts 30 "3-414 by the cut-ofirelay I10. The length of the printing impulses and the synchronizingimpulses is thus determined by the setting of the cut-off relay I10, andthis relay is in practice adjusted to cut-ofishortly before the termina-36 tion of the line signal. In this way, the circuit is normally brokenat contacts I13-I14, which may be provided with a spark suppressorarrangement to suppress sparking at these contacts. With perfect unison,the circuit is broken before the 40 brushes leave the connected segment,hence sparking at the distributor is minimized, such.

sparking as occurs being principally due to the inductive energy in thekey magnet. The sparking at the contacts of the key switches is neg- 45ligibie.

It is to be observed that when receiving printing signals, the keymagnet energized is that which is connected to the segment beingcontacted by brush arm I3. When the brush arms 59 at the sending andreceiving stations are in unison, the key magnet selected at thereceiving station will correspond with the key switchclosed at thereceiving station. Accuracy in selection thus depends on close unison ofthe brush arms,

5 and cutting oil the printing impulse before the brush arm at thereceiving station has carried over into contact with the adjacentsegment. The corrector magnet provides the required close unison, andthe cut-off relay terminates the im- 00 pulses, both synchronizing andprinting, after a definite interval. The line retardation and ionizingtime of the electronic relay are not material factors with the presentinvention, since the synchronizing signals are subject of the same delayas are the printing signals, and the corrector I magnet automaticallycompensates for this delay. Likewise, any instrumental delays fromlinerelays, etc. interposed in the transmission system are automaticallycompensated for.

10 While 'forillustrative purposes, the sending Calling circuits andoperations Referring to Fig.-4,-which shows the calling circuitsseparated from the other circuits, the

apparatus receiving the calling signals from the line include theartificial line AL, and the pri- 10 mary 33 of the input transformer 32.The apparatus for utilizing the calling signals comprise the .secondary34 of the input transformer, the glow lamp 202, the electronic relayI32, the cutout relay I10, the send-receive switch I9Il,.and 15 the callbell I. The send-receive switch I30 controls the calling circuit. Whenthe send-receive switch is in either the ,typing or sending positions,the call bell is connected in the calling circuit; when the send-receiveswitch is in the 2 receiving position, the call bell is disconnected.

Assume the send-receive switch at the receiving station is in a typingposition and that the machine is being used for typing purposes. Tocall, the sending station throws the send-receive switch to the Sposition and sends synchronizing signals to the line as described undersynchroni zation. From terminals 3fl 3l of the receiving station, thesignals traverse the circuit from terminal through primary 33 throughartificial 30 line AL to terminal 3|. Some current flows throughsecondary 29, but the primary 28 is open, and this current isineffective. The signal impulses through the primary 33 induce potentialvariations in the secondary 34 and these varia- 35 tions are applied tothe grid I33 as previously described. The grid I33 ionizesthe electronicrelay I32 which becomes conducting, and a circuit is completed from zerobus I3I through elecwinding I" of cut-oil relay I1Il,.via contactsI94I93 through winding of the call bell 2M. to

positive bus 25. Current flowing in this circuit energizes the callbell, and also cut-oii relay I10, which operates and breaks the circuitin the usual way. This action is repeated as each synchronizing impulseis received. Since the cut-off relay opens the circuit after each pulse,the interrupter in the bell can be dispensed with.

To stop the bell, the send-receive switch is '50 thrown to the receiveposition which opens the calling circuit, and establishes the receivingcircuit as shown in Fig. 3. The receiving distributor is thensynchronized, as previously described, and transmission begins. '55

The second calling situation is that existing when a station is sendingand the receiving station wishes for some reason to call back. This isthe so-called break-in" call, Referring to Figs. 2 and 3, the circuitconditions at the sending station are shown in Fig. 2, those at thereceiving station in Fig. 3. To make the break-in signal, the receivingstation throws the send-receive switch to the send position, changingits circuit conditions to those shown in Fig. 2, and syn- I15 chronizingsignals are immediately sent to the line in the reverse direction, i.e., from receiving I station to sending station. The calling circuit atthe sending station is in the condition shown in Fig.4, the send-receiveswitch being in the position shown by dotted lines. Due to the duplexarrangement ofthe transformers, previously described, the receivedsynchronizing signals actuate the electronic relay I32, and the callbell is energized as previously described. Due to the I balancing effectof the artificial line, the outgoing signals do not actuate theelectronic relay. Without further analysis, it will be evident that acalled station can acknowledge the call, and signal ready, by throwingthe send-receive switch momentarily to the send position in answering acall, and before moving to the receive position. The calling station isthus informed of the readiness of the called station, and can startsending without delay. 2

In the foregoing, the call signal device was described as a bell. It isobvious, however, that any of the usual audible or visual signallingdevices, such as buzzer-s, gongs, annunciators, lamps, etc., can beemployed, the power in the calling circuit being adequate for operatingsuch devices and such variations are included within the scope of theinvention as defined by the generic claims.

It will be observed that in the foregoing description of the callingsystem, two-way communication circuits were assumed. When onewaycircuits, such as radio circuits, are employed, break-in and call-backsignals are not usually feasible and the usual calling conventions forone-way circuits must be observed.

It is further to be observed that with the calling system described, itis not necessary that the distributor motor beturned on, but that powermust be supplied to the electronic relay. To receive a'calling signalwithout having power on the electronic relay, a small neon .glow lamp202 is connected into the calling circuit at some convenient point, asfor example across the second-,.

ary 35 as indicated in Fig. 4.

It will be perceived that I have provided a simple and flexible callingsystem which is very economical in cost, and which possesses numerousadvantages.

The electronic relay The electronic relay I32 may be of the hot cathodetype, as shown, or of the cold-cathode type, in which case the cathodeheating transformer I3! is not required. As is well known, the gridpotentials suiflcing to ionize electronic relays is comparatively low,and they are therefore susceptible to stray potentials. inductiveeffects, etc. and for best results, measures to insure stability inoperation are desirable. In the present invention, stabilizingmeasureswhich have been found effective comprise the grid currentlimiting resistor 203, the grid to cathode by-pass condenser 204, andthe grid potential stabilizer arrangement consisting of the ballastcondenser 205 and the ballast resistor 206.

The function of the current limiting resistor 203 is to limit the gridcurrent to moderate amounts during the periods when the grid ispositive. It is preferably of a comparatively high value, values of50,000 to 500,000 ohms giving good results. The function of the grid tocathode by-pass condenser 204 is to by-pass high frequency and inductivepotentials, preventing ionization of the relay from these effects. Thiscondenser may be of comparatively small size, capacities of the order of.0025 mfd. having been found to give good results.

I86 is lost, and current flowing through bias resistor 24b to replenishthe charge on condenser 86 causes a momentary variation in drop across24b. The potential across ballast condenser 20S, and consequently'thegrid bias potential, remain almost constant during such variations,since because of ballast resistor 206, any change in the charge oncondenser 205 is retarded. The time constant of the combination ofcondenser 205 and resistor 206 is proportional to the product of Therotary distributor and phase corrector In Figs. 5 and 6, which show indetail the rotary distributor and corrector magnet assemblies, therotary distributor is seen to consist of a hub 31, with diametricallypositioned contactor arm 38 and corrector arm 39 mounted in cross holes40 therein by suitable holding means such as set screws 4|. On thecontactor arm 38 is mounted a link 42 of insulatingmaterial by means ofscrew 43, extending axially into the outer end of contactor arm 38. Onthe project- 'ing end of link 42 is mounted the brush arm l3 by means,of a screw 44, extending axially .into arm l3. The outer end of the armI3 is cut into half-cylindrical section, and on the cut section ismounted the half-cylindrical brushclamp 45. Between the flat surface ofarm I! and clamp 45 are clamped two flexible metallic brushes 46 bymeans of a screw 41. The outer ends of the brushes 4B slope rearwardlyand contact the segments II and ring l2 with a lightpressure. Thebrushes are conveniently made of copper braid, bundles of small copperwires,

' or silver strips, as is commonly practiced in the telegraphic art.

The corrector arm 39 carries at its outer end the corrector bar 49 ofmagnetic material, preferably a metal or alloy of low magneticpermeability such as soft pure iron, or magnetic nickel alloy. Thecorrector bar may have a variety of shapes, the preferred shape beingshown in Figs. 6' and 7. The corrector bar should be rigidly mounted onthe corrector arm, and is so mounted conveniently by positioning in aslot cut in the end of the corrector arm, and secured therein by one ormore screws 48 (one being shown)- as clearly indicated. In the preferredform, the location and length of the corrector bar 49 is such that onrotation of the distributor hub, the corrector bar passes end-wisebetween the pole pieces 50 with a small air-gap at each end. The air-gapwhich has been found preferable is of the order of .025 inch. Thecorrector magnet 36 is preferably mounted on a bracket 52, adjustable inan are by means of curved slots 53 and screw 54, so that the poles 50 ofthe corrector magnet 36 may be adjustable sidewise concentrically withthe drive shaft 55. By this adjustment, the corrector magnet 36 may bemoved in relation to the synchronizing segment I. The need for thisadjustment will be evident when it is considered that a small intervalof time is required for the flux 7 in the corrector magnet 36 to buildup in response to the synchronizing current impulses, this interval inpart depending upon the induct-' ance in the corrector magnet circuit.During this small interval, the distributor arm moves in the directionof rotation, hence the'corrector magnet for proper action should bedisplaced angularly in the same direction by a slight amount arcane inexcess of the mechanical angle of 180 represented by the axis of thecorrector arm and the The best proportions for the faces of the polesofthe corrector magnet, and forthe corrector bar may be in partdeterminedby analysis,..but refinement in the design of these parts ismost readily obtained by experiment, The result desired is that thecorrector bar should pass between the poles of the corrector magnetwithout material retardation or acceleration when the distributor arm isin perfect synchronism with that of the sending station, but shall besubject to corrective action when the synchronous relation is departedfrom.

Figs. 8 and 9 show a modification of the corrector bar-corrector magnetarrangement, in

which the corrector 49 passes in front of the poles 50 of the correctormagnet 36. The poles 58 are in this case narrowed at the face nearestthe corrector bar to substantially the width of the corrector bar,- asshown. On analysis, it will be evident that as the corrector barapproaches or departs from the poles G, a tangential magnetic pullwill-be exerted. The correcting action will therefore be the same as forthe forms shown in Figs. 6 and '7. The strong radial pull, however,requires increased rigidity for the drive shaft to resist thisunbalanced pull. This unbalanced radial pull, together with the factthat the correctorsbar 49 of the form shown in Figs. 8 and 9 is for thesame magnetic efliciency heavier than that shown in Figs. 6 and 7represent.

comparative disadvantages for the first .named type.

Another possible modification of the form of the corrector bar andcorrector magnet poles is shown in Figs. 10 and 11. Since thismodification represents a combination of those previously discussed, itsaction is manifest and further discussion' is unnecessary.-

Various other combinations of pole pieces and corrector bar shapes arepossible, and such variations are included within the scope of theinvention-as defined by the generic claims.

Fig. 12 shows atypical tangential magnetic pull-displacement curve. Theordinates represent, in arbitrary units, the tangential component of themagnetic attraction of the poles 50 on the corrector bar 45 shown inFigs. 6 and 7. The abscissae represent the displacement of the verticalmedian plane of the corrector bar from the median plane of thecorrectormagnet poles. The arrows within the diagram indicate that %the pull istowards the median plane of the corrector magnet. From this curve it'isevident that a tangential force tends to hold the corrector bar inalignment with the corrector magnet poles.

Assuming-the corrector magnet to be energized 'by uniform directcurrent, this force depends on the amount ofthe displacement of thecorrector bar from the median plane of the corrector poles, increasingrapidly to a peak value and then declining. For exact coincidence of thepoles. some'distortion of curve doubtless occurs. Also, thesynchronizing current impulse is of a general sine-wave form,causlngfarise and fall in the magnetizing force of the-magnet. Practicalexperience indicates, however, .that the curve shown in Fig. 12represents substantially the corrector-bar is rapidly between the .thecorrective action of the corrector magnet on the corrector bar tomaintain the latter in unison with the sending distributor arm.

Referring to Fig. 6 which shows details of the drive shaft hub assembly,the hub 31, preferably made of a light metal such as aluminum, has acylindrical axial bore 56 fitted to gtve a free turning fit onthedrive-shaft. A drive collar 51 lindrical cavityqinthe lower end ofthehub 37.

and is adjustably secured therein by any preferred means, as .bythe setscrew 66. Assembled on the hub collar 62 next. to the hub is the stopflange 65, being secured thereto by welding or other preferred means.The stop flange is extended radially at one point on its periphery toform an ear es as shown. .The purpose of this construc-' tion is topermit of ready angular adjustment of the ear 65 on the stop flange65 inrelation to the distributor arm to enable proper setting of the restposition of the brushes 66 to be made.

To the top of the hub H is demountably assembled the friction cup Bl,held from rotating counter-bored to contain a friction pad 68 of softmaterial, preferably a firm felt ring. The upper end of the driveshaft55 is reduced in section and is threaded. Thereon is screwed theadjustable friction nut 69, provided with a radial set screw it toretain the friction nut in the position of adjustment.

The friction pad se is liberally oiled and on being compressed, oilworks down the shaft along the bore of the hub to the friction washer 6!to provide lubrication of these parts. The friction nut is adiusteduntil the distributor arm is driven with little if any slip. Thearrangement shown permits of an easily adjustable, smooth actingfriction drive for the, distributor arm which is found to stay inadjustment for extended periods.

v The clutch mechanism Referring to Figs. l3, 14, 15 which-show theassembly of mechanism by which synchronism is established-adjacent tothe rolls 59 and 63 and .with axis parallel with the shaft 55 isrotatably mounted the double cam 12 located so as toengagecircumferentially the rolls 59 and- 63. The cam 12 rotates on thespindle I3 mounted perpendicularly on plate it by riveting. Underneaththe cam I2, slidably mounted on plate 14, is the cam detent 15. The camdetent l5 pivots. at one end on the pivot pin 18. In the middle sectionof the cam detent is a curved slot 11, through. which extends thestudscrew 18. This screw prevents the cam detent from rising out of placeand limits its travel. The free end of the cam detent is bifurcated, andthe two prongs turned up toform pawls 80 and 8| which alternatelyengage-the lower stop 82 on the double cam 12. Extending through the camdetent 15, between the slot "and the pin 16, is located a small hole 83,through which is assembled the crank-shaped end of the operating ilnk84. The other end of link 84 is threaded and to it is assembled theadjustable clevis 85. The clevis 85 is assembled to the armature l6ofthe release relay 5 by a pin 86.

The cam 12 is provided with a projecting upper stop 81, located on thetop surface, and diametrically opposite the lower stop 82. This upperstop 81 is engageable by the ear 66 of the stop flange 65 in oneposition of the cam 12. The diameter of the cam 12 is reduced at themiddle by the groove 98 (see Fig. 16). Extending into and across thegroove 98 is the accelerating spring 9| which bears near its outer endagainst the accelerating pin 92, as shown. The accelerating spring 9| islooped in several turns around a pin 93 rigidly mounted in the plate 14.The fixed end 94 of the accelerating spring 9| bears against the pivotpin 16. The accelerating pin is so formed that when assembled as shown,the free end bears with moderate pressure against the accelerating pin92.

The circumference of the double cam is serrated with a straight knurlexcept over an arc of approximately 90 in the region of the upper stop81, where the radius is reduced and the cam edges are left smooth. Thisare of the cam clears the rolls 59 and 63 when adjacent thereto.

The operation of the clutch mechanism is as follows: When the parts ofthe mechanism are in the position shown in Fig. 13, the short pawl 88engages the lower stop 82, stopping the double cam in such position thatthe upperstop 81' is virtually on the line of centers of the rolls 59and 63 and the double cam 12. In this position the smooth edge of thecam is adjacent the rolls 59 and 63, providing clearance therebetween.The

. hub 31 can therefore continue rotation until the ear 56 engages theupper stop 81, which stops the motion of the hub and the brush arm isstopped in the rest position on segment 3 as shown in Fig. 5. Since thehub 31 is frictionally driven, the drive shaft 55 and the roll 59continue in rotation.

Assuming now that the release relay I5 is ener gized, the armature l6pulls the link Bd which in turn draws the cam detent 15 away from thecam. The short pawl is thus pulled out of engagement with the lower stop82, releasing the cam 12. The detent 15 is drawn to the position shownin Fig. 14. The accelerating spring 9| by exerting force on theaccelerating pin 92 causes the can: 12 to rotate quickly in acounterclockwise direction. This rotation of the cam 12 brings itsserrated edges into engagement simultaneously with rolls 59 and 63.Since roll 59 is securedto the drive collar 51, and roll 63 to the hubcollar 62, when the cam serrations grip the rubber rolls '59 and 63, thehub 31 is virtually locked to the drive shaft. It is to be noted thatthis is not a friction clutch, since the serrated cam edges mesh withthe rolls 59 and 63 without slipping and as though geared thereto.

The cam 12 isrotated by reason of' being engaged by roll 59, and theupper stop 81 is rotated away from the car 66, removing these membersfrom engagement. The cam 12 continues-to rotate until it reaches theposition shown in Fig. 14, when the lower stop 82 comes into engagementwith the long pawl 8|, stopping the cam. In this position the smooth arcis adjacent the rolls 59 cuit, comprising part of the and 63 and the hub31 is freely driven by the friction drive previously described. The ear66 link 84 pushes the detent 15 back into the position shown in Fig. 13,disengaging pawl 8| andlower stop 82. The accelerating spring 9|, whichhas been placed in tension on the accelerating pin 92 by the rotation ofcam 12, now rotates cam 12 through a short arc, bringing cam 12 in theposition shown in Fig. 13. When the ear 66 arrives at the upper stop 81,the hub is stopped and conditions are restored as at the beginning ofthe cycle described above. It is to be observedthat the mechanism justdescribed provides'a definite, but adjustable, stop or rest position forthe brush arm I 3; that on operation of the release relay l5 the drivingshaft 55 and hub 31 are quickly clutched together in a positive mannerto bring the hub 31 up to the speed of the driveshaft; that the-positiveaction of a gear clutch is obtained without the difficulty of possibleclashing of gears if engaged in the wrong position; and that the clutchaction is controlled with the application of but little force on thepart of the clutch release magnet; The accelerating spring 9| minimizesthe interval required for the clutch to act after the release relay isenergized.

It is obviously possible to eliminate the clutch mechanism and cause.the link 84 to engage and stop the ear 66 without the intervention ofadditional mechanism. The frictional torque of the friction drive is,however, restricted to a small amount, otherwise the pull of thecorrector magnet 36 will be insufficient to overcome the frictionaltorque. The proper frictional torque for good correcting action isincapable of accelerating the hub 31 and the distributor 'arms mountedthereon without considerable slip occurring. Furthermore, in practice itis found that such slip during acceleration is variable to such anextent that the corrector arm bar 49 does not reliably come intoposition between the poles 58 when the hub is accelerated solely by thenormal frictional driving torque. The object of the clutch mechanism istherefore to establish synchronism in a single revolution in a certainand reliable manner.

The release-relay Referring to Figs. 13 and 17, which show the releaserelay l5 and associated parts of the cirpresent invention, the relayproper is of a well known type, commonly referred to as a telephonerelay. On the core I5 is assembled a low resistance coil 20 of acomparatively few turns concentrated at the armature end of the core.Next in order is a high resistance winding 2| of several thousand turns,occupying the central part of the core length. At the heel end of thecore is assembled'a concentric sleeve or slug of copper 23. The coils 20and 2| are wound in the same direction and the' adjacent terminals ofthe windings are connected together in series connection.

The release relay as thus far described is a well known type commonlyclassified as a doublewound slow releasing relay. When supplied with apulse of sufficient magnitude and of considerable duration, such relaysnormally operate in from .004 to .006 second, and release in from .08

to .28 second after being fully energized. In high is speed printingtelegraphs, however, the signal impulses are of very short duration, thecomplete pulse interval being of the order of "-003 to .005

second. A relay of the usual type designed to have a release time of .25to .30 second, i. e. the time required for the distributor arm to makeone revolution, plus a margin, will not respond to impulses of shortduration, for the reason that the copper slug required to produce suchdelay in release time is of comparatively large size, and prevents byits reaction the storing of the required amount of magnetic energy inthe magnetic structure of the relay. To overcome this difiiculty, whichis inherent with this type of relay, a storing condenser 22 is connectedin shunt across the terminals of the high resistance winding 2|. Thiscondenser should normally be of considerable capacity, values of from 2to 16 microfarads, depending on the release time desired, having beenfound to give good results. with this condenser added to thecombination, the operation of the release relay IS in response tocurrent impulses of short duration is'as follows: When the synchronizingpulse is applied to the circuit shown in Fig. 17, a rush of currentflows through the low resistance coil 20 into the storing condenser 22,which because of its large capacity offerscomparatively little impedanceto such rush of current, particularly at the beginning. This rush ofcurrent through coil 20 magnetizes the core I5 at the armature end andattracts the armature I6. The reaction of the high resistance coil 2|and the slug 23 are inefiective to prevent the coil 20 from magnetizingthe armature end of the coil I5, because of their remoteness from thissection of the core, and because of the high inductance of the coil 2|.The counter E. M-. F. generated by transformer action in coil 2| by thecurrent in coil 20 does not oppose the current in coil 20, but isutilized to aid in charging condenser 22. The maximum energy is thusstored in the charge of condenser 22. On the decay of the pulse current,this energy, combined with that 1 stored in the coil 2| and the slug 23,operate to maintain the magnetic flux in the core, in accordance withLenzs law. The armature is thus held firmly to the core during the decayof the pulse and thereafter. The release time is controlled by theamount of charge on the condenser 22 and the time required for thecurrent through coil 2|, due to this charge, to decay until the holdingcurrent in the coil 2| drops below minimum value. The variable resistorI9, located in the circuit as shown in Fig. 17, provides a convenientmeans for adjusting electrically the release timeof the relay withoutthe necessity of change in design, or mechanical adjustment of therelay. It is to be noted that the location of resistor IS in the circuitis such, as not to interfere with the operating pulse, but acts only toretard the discharge of condenser 22 through the coil 2I-. Where suchadjustment of the release time is not required, the resistor 22 may beomitted without detriment, provided the resistance required to producethe release time desired is incorporated in the coil 2|.

It is to be noted that the role of the slug 23 is materially differentin the present invention from that played in the types of slow releaserelays heretofore known. 'In such prior types, the

release time is mainly dependent on the energy induced in the slug'(stored in the form of circulating current) by change in the magneticflux in the core I5. In the present invention, the release time iscontrolled almost exclusively by the charge on the condenser 22 and thecharacteristics of the coil -2 I, any contribution from the slug beinginconsequential. For certain values of capacity of the condenser 22 andof inductance and resistance of the coil 2|, an oscillatory discharge ofenergy between the condenser 22 and coil 2| may occur. For othercombinations, a reversal of flux may occur when the circuit includingthe windings of the release relay is broken. In such instances the relaymay release the armature I6 momentarily, causing an unwanted drop out.The slug 23, by its damping action, opposes sudden magnetic changes, andcauses the relay to hold without chatter or release during transientconditions in the circuit. The damping action of the slug 23 is ofimportance in cases where the relay tends to. chatter or drop outmomentarily. In cases where such tendencies do not exist, the slug 23may be dispensed with. I

The relay describedis capable of quick operation when supplied withimpulses of short duration; of holding firmly over periods of as much asa second after the energizing current has been cut oil; and of beingreenergized by short current pulses recurring periodically. It isfurther characterized by the principle of storing the energy forholdingthe relay in an operated condition is an associated condenser, whichcondenser is charged partly by the pulse current'and partly byenergygenerated in the holding winding by transformer action from theoperating winding. The characteristics and principle of operation ofthis relay are such as to constitute a generic class distinguished fromprior forms of quick acting, slow release relays. 1

The motor governor Referring to Figs. 18 to 21 inclusive, the motorgovernor I00 which is of the electrical type,

consists of a disk IOI of insulating material,

mounted on a hub I02, which in turn is mounted on the motor shaft I03 byset screw I04. On the periphery of the disk IOI are mounted two sliprings, I04 and I05, by which means current is v upturned portion of thebracket I01 is threaded the adjustable contact screw III having at theend a contact I I2.

The governor bracket I08 mounts the kinetic members, namely, the tongueH3 and the governor spring Ill. The tongue H3 is ofspecial construction,consisting of .a flexible strip 5, and a. bi-metal strip IIB securedtogether by rivets In, as shown (see Fig. 20). As is well known,bi-metal consists of sheets of two metal or dissimilar co-eflicients ofexpansion, usually welded together to form one laminated sheet or strip.It has the property of exhibiting curvature when heated, the degree ofsuch curvature being to a certain extent proportional to the change intemperature from the particular temperature at which the bi-metal isfiat or straight. Metals commonly used in producing bi-metal are brassand steel, and brass and Monel metal.

At the outer end of the bi-metal strip H6 is mounted the movable contact8', positioned to lie fiat against the stationary contact II2 when theirsurfaces are in contact. The ton ue II! is conveniently mounted on asupport I20 by means of a screw l2l and clamp I22. The support I20 ispart of the governor bracket I08. Near the middle of the tongue is ahole into which is inserted the swivel pin I23, having a hole into whichis threaded one looped end of the governor spring Ill. The governorbracket I is mounted on the disk MI by two screws H9 at one end, whichscrews terminate in the slip ring I making electrical contact therewith.The contact bracket I01 and the governor bracket I08 are insulatedelectrically, except when the contacts I I2 and H8 are closed. A portionof the governor bracket I08 is upturned to form the support I24 uponwhich is mounted the flexible adjusting lever I25. The free end of theadjusting lever is turned inwardly and is perforated by a small holeinto which is threaded a looped end of the spring I I4 as shown. Betweenthe bent portion of the adjusting lever I25 and the support-.124, theadjusting lever is pierced by a hole, through which is assembled themicrometer adjusting screw I26, screwed into the support member I21,

The operation of the governor is as follows: Assume that the governor isrotating in a counterclockwise direction as viewed in Fig. 18. At aparticular speed, the centrifugal force on the tongue 3 will exceed thespring tension in the spring H4, and the contacts II2-II8 will open.When these contacts open, the resistance R2 is inserted in series withthe motor as shown in Fig. 21. The motoris thereby slowed down, causingthe contacts to close, again speeding up the mo tor. This process isrepeated many times a second, the motor not reachinga stable speed, butvarying minutely above and below the speed at which the. contacts open.This type of governor, is well known, and it is to be observed that boththe inertia of and centrifugal force on the tongue II3 contribute to theregulating action. It has therefore been called a centrifugal-inertiagovernor. It is characterized by its sensitivity and accuracy ofregulation.

The novel-features of the present invention reside in the means fortemperature compensation and for minorspeed adjustment. It is evidentthat the tension in the spring H4 determines the speed to which themotor is regulated. An increase in the temperature of spring I I4results in a slight decrease in its tension, lowering slightly theregulated speed of the motor. This effect is compensated for in twoways. The governor bracket I08 is held in position at one end by screwsI I9, the other end being free to move endwise only. The tensioninglever I25 and the adjusting screw I26 are mounted at the free end of thegovernor bracket I08. As the temperature of the governor increases, thegovernor bracket I08 is extended endwise by thermal expansion,stretching to a slight extent the spring I I4, thereby increasing itstension and compensating in part for the decrease in tension due totempera ture. The compensation gained by this means is limited, however,by the thermal expansion of the material of the governorbracket alongits 'length, and since the length of wire in the spring is much greaterthan the length of the governor bracket, compensation over aconsiderable range of temperature is not readily accomplished by thismeans alone. The second temperature compensation means is provided bythe bi-metal strip II6 forming part of the tongue II3. As shown in Fig.20, in exaggerated form, when the temperature of the bi-metal strip H6is increased, it curves convexly outward. Due to this curvature, thetension of the spring I I4 is increased with increase of temperature,compensating for its normal loss of tension with increase oftemperature. By using proper bi-metal combinations and proportions ofparts, determinable by well understood methods, thermal compensation ofthe governor may be accomplished over a considerable range oftemperature. With this improvement, the type of governor shown willregulate the speed of the motor with a high degree of precision undervarious conditions of temperature.

Minor speed adjustments It would appear that the resistance R2, commonlycalled the gap resistance, if sufliciently large to slow the motor downto the speed set by the governor, would have little 'efiect on the speedset by the governor. Such is the case, but a minor change in speeddoesresult from a comparatively large change in the value of theresistance R2. According to the present invention, this effect isutilized to accomplish minor adjustment of the motor speed, withoutmechanical adjustment of the governor, the value of R2 being variablefor that purpose.

It is to be noted that changing the value of the gap resistance R2 isnot equivalent to introducing a similar resistance into other parts ofthe motor circuit. Resistance placed in series with the motor, forexample, has the same effect as a change of load, and is counteracted bythe governor. The effect of such series resistance is also to impair therange of regulation of the governor. A relatively large change in thegap resistance R2 does not limit to any material extent the range ofregulation of the governor, but does produce a minor change in the speedset by the governor.

In printing telegraph systems, it is sometimes desirable to cause thesending instrument to run slower by a constant amount than does thereceiving instrument, or vice versa In the present invention a change inthe gap resistance is utilized to effect the desired constant speeddiflerence. For this purpose, as resistance RI is placed in series withthe variable gap resistance R2 but is normally short circuited by thecontacts I 09-I09. When these contacts are closed, the motor speed isregulated by the governor gap re-. sistance R2 as previously described.When the contacts are open, additional resistance is introduced in. thegap, and minor but constant decrease in speed results. It is obviousthat the same arrangement, considering as normal the speedwhen contactsIDS-I09 are open, will produce a minor increase in speed when thecontacts IDS-409 are closed. The contacts IDS-I09 may consist of aswitch, for local operation, or of the contacts of a relay for remotecontrol.

It is thus clear that the present invention provides a novel method oftemperature compensation and minor speed control and adjustment for anelectrical governor. The improved governor herein described is highlyaccurate, rapid and sensitive in action, self-compensating fortemperature changes, adapted to minor speed adjustments without stoppingthe governor or changing its mechanical adjustments, and particularlyadapted to control of incremental speed changes by remote control.

Spring link feature As previously stated, the signal impulses andoperation impulses in a high speed printing telegraph are very brief induration, and special provisions are necessary to assure certainresponse of relays and magnets to such brief impulses.

One of the features of the present invention 15

